Endotracheal tubes have been routinely used for a number of decades to prevent upper airway obstruction or to facilitate artificial ventilation of unconscious or anesthetized patients. Early designs of endotracheal tubes consisted of a relatively pliable tube shaped for insertion through the oral passage and into the trachea, and adapted to connect to a respirator for the introduction of air into the lungs. To avoid the escape of air from the trachea out the oral and nasal passages, improved endotracheal tubes were later introduced which included an inflatable bag-like structure or cuff disposed about the exterior surface of the tube at the distal end. These newer endotracheal tubes, which are in common use today, are inserted into the trachea such that the cuff is disposed a few centimeters below the larynx. Once in place, the cuff is inflated by a source of air and creates an airtight seal between the tube and tracheal wall. This effectively prevents air being pumped by a respirator into the lungs from escaping the trachea and entering the oral and nasal passages.
Further research resulted in the development of two-cuff endotracheal tubes which generally consist of an esophageal cuff and an oral cuff. Properly positioned in a patient, the two-cuff endotracheal tubes are operable to seal the esophagus and prevent the contents of the stomach from entering the lungs, while also preventing the escape of air being pumped into the lungs from the trachea.
These improvements of endotracheal tubes have encouraged physicians to prescribe prolonged endotracheal intubation of from several days to two or more weeks for some patients. However, particularly over longer intubation periods, several problems have been identified in the use of existing endotracheal tube designs. It was discovered that in an effort to create a non-leak seal between the cuff and walls of the trachea that the pressure applied by the cuff had a tendency to damage the ciliated endothelium of the trachea and occlude the blood perfusion of the tracheal mucosa after a period of time leading to tissue necrosis. In addition, it was found that some patients experienced laryngeal dysfunction due to contact of the endotracheal tube within the posterior endolarynx.
Initial studies of the problems encountered in the use of known endotracheal tubes resulted in attempts at improved designs such as disclosed in U.S. Pat. No., 4,091,816 to Elam. The Elam patent discloses an endotracheal tube with a double cuff arrangement wherein a standard cuff is mounted on the exterior surface of the tube adjacent its distal end, and a second cuff is disposed upwardly along the tube from the lower cuff. The two cuffs are interconnected so that air pumped into one cuff may be transferred to the other. With the endotracheal tube of Elam properly positioned in a patient, the lower cuff is disposed a few centimeters below the larynx within the mid-trachea and the upper cuff a few centimeters above the larynx.
The interconnection between the two cuffs in the Elam patent is intended to solve the problem created by overpressurizing the single cuffs found in prior art endotracheal tubes to avoid damage to the ciliated endothelium of the trachea and possible tissue necrosis. The volume of air in the lower cuff which seals the trachea is transferable to the upper cuff to avoid undue pressure on the tracheal walls while maintaining an airtight seal between the tube and tracheal walls.
In addition, the Elam patent suggests that laryngeal dysfunction is brought about by contact of the endotracheal tube with the vocal cords of the larynx, particularly as a result of the to-and-fro motion of the tube induced by the operation of the respirator as it provides air to the lungs. To reduce the abrasion to the vocal cords caused by such tube motion, the two cuffs along the Elam endotracheal tube are deliberately placed on either side of the larynx. This arrangement is intended to anchor the tube in relation to the larynx so as to prevent or at least limit the to-and-fro movement of the tube against the vocal cords.
Careful study of the effects of prolonged endotracheal intubation has provided a much more accurate appreciation of the true cause of laryngeal injury than suggested in the prior art. It is clear that laryngeal dysfunction is brought about by mechanical trauma of the endotracheal tube as it rides within the posterior endolarynx. This mechanical trauma is imposed by constant and ongoing forces applied by the tube which are related to respirator-induced tube movement, patient movement and reflex laryngeal movement against the tube.
Importantly, it has been discovered that such mechanical trauma is directed to a large extent against the arytenoids and in particular the cricoarytenoid joint and surrounding tissue where the endotracheal tube actually rests when properly positioned in a patient. As an inherent result of the shape of existing endotracheal tubes, the cricoarytenoid joint region becomes a fulcrum or pivot point about which the tube pivots and moves in response to forces applied to the tube by operation of a respirator or by movement of the patient's head and neck.
It has been observed and determined that the resultant effect of such mechanical trauma is potentially serious laryngeal dysfunction. One specific form of laryngeal dysfunction observed is the initiation of traumatic cricoarytenoid arthritis. While generally not permanent, even transient laryngeal dysfunction resulting from cricoarytenoid arthritis may be serious to some patients. As has been documented, the development of cricoarytenoid arthritis may result in a loss or impairment of the laryngeal sphincteric function wherein the cricoarytenoid joint fails to fully close the tracheal tube during swallowing or open during respiration. Without proper sphincteric function to fully seal the trachea, aspiration may occur with the accompanying adverse pulmonary effects. Aspiration is always dangerous, but it can be catastrophic for an already accutely or chronically ill patient with minimal reserves. Failure of the cricoarytenoid joint to fully open may result in a compromised airway into the trachea where the vocal cords do not move open because of the injury to the joint and surrounding tissue. In some cases, injury to the cricoarytenoid joint and surrounding tissue may result in permanent scarring. Any scarring at this site is extraordinarily difficult to correct surgically and may necessitate a permanent tracheotomy.
It is therefore an object of this invention to provide an improved endotracheal tube which eliminates or at least reduces laryngeal dysfunction.
It is another object of this invention to provide an improved endotracheal tube capable of cushioning and protecting the cricoarytenoid joint region including the vocal process and body of the arytenoids, the interarytenoid spae and the intraluminar surface of the cricoid in its porterior one-half, to assure proper laryngeal sphincteric function upon extubation of the tube.
It is a further object of this invention to provide an improved tracheal tube having the dual capability of sealing the trachea without damage to the tracheal walls while protecting the cricoarytenoid joint region from trauma.